This module implements a pretty-printing facility to format text
within 'pretty-printing boxes'. The pretty-printer breaks lines
at specified break hints, and indents lines according to the box
structure.

You may consider this module as providing an extension to the
printf facility to provide automatic line breaking. The addition of
pretty-printing annotations to your regular printf formats gives you
fancy indentation and line breaks.
Pretty-printing annotations are described below in the documentation of
the function Format.fprintf.

You may also use the explicit box management and printing functions
provided by this module. This style is more basic but more verbose
than the fprintf concise formats.

use simple break hints (as obtained by print_cut () that outputs a
simple break hint, or by print_space () that outputs a space
indicating a break hint);

once a box is opened, display its material with basic printing
functions (e. g. print_int and print_string);

when the material for a box has been printed, call close_box () to
close the box;

at the end of your routine, flush the pretty-printer to display all the
remaining material, e.g. evaluate print_newline ().

The behaviour of pretty-printing commands is unspecified
if there is no opened pretty-printing box. Each box opened via
one of the open_ functions below must be closed using close_box
for proper formatting. Otherwise, some of the material printed in the
boxes may not be output, or may be formatted incorrectly.

In case of interactive use, the system closes all opened boxes and
flushes all pending text (as with the print_newline function)
after each phrase. Each phrase is therefore executed in the initial
state of the pretty-printer.

Warning: the material output by the following functions is delayed
in the pretty-printer queue in order to compute the proper line
breaking. Hence, you should not mix calls to the printing functions
of the basic I/O system with calls to the functions of this module:
this could result in some strange output seemingly unrelated with
the evaluation order of printing commands.

Boxes

val open_box : int -> unit

open_box d opens a new pretty-printing box
with offset d.
This box is the general purpose pretty-printing box.
Material in this box is displayed 'horizontal or vertical':
break hints inside the box may lead to a new line, if there
is no more room on the line to print the remainder of the box,
or if a new line may lead to a new indentation
(demonstrating the indentation of the box).
When a new line is printed in the box, d is added to the
current indentation.

val close_box : unit -> unit

Closes the most recently opened pretty-printing box.

Formatting functions

val print_string : string -> unit

print_string str prints str in the current box.

val print_as : int -> string -> unit

print_as len str prints str in the
current box. The pretty-printer formats str as if
it were of length len.

val print_int : int -> unit

Prints an integer in the current box.

val print_float : float -> unit

Prints a floating point number in the current box.

val print_char : char -> unit

Prints a character in the current box.

val print_bool : bool -> unit

Prints a boolean in the current box.

Break hints

val print_space : unit -> unit

print_space () is used to separate items (typically to print
a space between two words).
It indicates that the line may be split at this
point. It either prints one space or splits the line.
It is equivalent to print_break 1 0.

val print_cut : unit -> unit

print_cut () is used to mark a good break position.
It indicates that the line may be split at this
point. It either prints nothing or splits the line.
This allows line splitting at the current
point, without printing spaces or adding indentation.
It is equivalent to print_break 0 0.

val print_break : int -> int -> unit

Inserts a break hint in a pretty-printing box.
print_break nspaces offset indicates that the line may
be split (a newline character is printed) at this point,
if the contents of the current box does not fit on the
current line.
If the line is split at that point, offset is added to
the current indentation. If the line is not split,
nspaces spaces are printed.

val print_flush : unit -> unit

Flushes the pretty printer: all opened boxes are closed,
and all pending text is displayed.

val print_newline : unit -> unit

Equivalent to print_flush followed by a new line.

val force_newline : unit -> unit

Forces a newline in the current box. Not the normal way of
pretty-printing, you should prefer break hints.

val print_if_newline : unit -> unit

Executes the next formatting command if the preceding line
has just been split. Otherwise, ignore the next formatting
command.

Margin

val set_margin : int -> unit

set_margin d sets the value of the right margin
to d (in characters): this value is used to detect line
overflows that leads to split lines.
Nothing happens if d is smaller than 2.
If d is too large, the right margin is set to the maximum
admissible value (which is greater than 10^9).

val get_margin : unit -> int

Returns the position of the right margin.

Maximum indentation limit

val set_max_indent : int -> unit

set_max_indent d sets the value of the maximum
indentation limit to d (in characters):
once this limit is reached, boxes are rejected to the left,
if they do not fit on the current line.
Nothing happens if d is smaller than 2.
If d is too large, the limit is set to the maximum
admissible value (which is greater than 10^9).

val get_max_indent : unit -> int

Return the value of the maximum indentation limit (in characters).

Formatting depth: maximum number of boxes allowed before ellipsis

val set_max_boxes : int -> unit

set_max_boxes max sets the maximum number of boxes simultaneously
opened.
Material inside boxes nested deeper is printed as an ellipsis (more
precisely as the text returned by get_ellipsis_text ()).
Nothing happens if max is smaller than 2.

val get_max_boxes : unit -> int

Returns the maximum number of boxes allowed before ellipsis.

val over_max_boxes : unit -> bool

Tests if the maximum number of boxes allowed have already been opened.

Advanced formatting

val open_hbox : unit -> unit

open_hbox () opens a new pretty-printing box.
This box is 'horizontal': the line is not split in this box
(new lines may still occur inside boxes nested deeper).

val open_vbox : int -> unit

open_vbox d opens a new pretty-printing box
with offset d.
This box is 'vertical': every break hint inside this
box leads to a new line.
When a new line is printed in the box, d is added to the
current indentation.

val open_hvbox : int -> unit

open_hvbox d opens a new pretty-printing box
with offset d.
This box is 'horizontal-vertical': it behaves as an
'horizontal' box if it fits on a single line,
otherwise it behaves as a 'vertical' box.
When a new line is printed in the box, d is added to the
current indentation.

val open_hovbox : int -> unit

open_hovbox d opens a new pretty-printing box
with offset d.
This box is 'horizontal or vertical': break hints
inside this box may lead to a new line, if there is no more room
on the line to print the remainder of the box.
When a new line is printed in the box, d is added to the
current indentation.

Tabulations

val open_tbox : unit -> unit

Opens a tabulation box.

val close_tbox : unit -> unit

Closes the most recently opened tabulation box.

val print_tbreak : int -> int -> unit

Break hint in a tabulation box.
print_tbreak spaces offset moves the insertion point to
the next tabulation (spaces being added to this position).
Nothing occurs if insertion point is already on a
tabulation mark.
If there is no next tabulation on the line, then a newline
is printed and the insertion point moves to the first
tabulation of the box.
If a new line is printed, offset is added to the current
indentation.

val set_tab : unit -> unit

Sets a tabulation mark at the current insertion point.

val print_tab : unit -> unit

print_tab () is equivalent to print_tbreak 0 0.

Ellipsis

val set_ellipsis_text : string -> unit

Set the text of the ellipsis printed when too many boxes
are opened (a single dot, ., by default).

By default, those tags do not influence line breaking calculation:
the tag 'markers' are not considered as part of the printing
material that drives line breaking (in other words, the length of
those strings is considered as zero for line breaking).

Thus, tag handling is in some sense transparent to pretty-printing
and does not interfere with usual indentation. Hence, a single
pretty printing routine can output both simple 'verbatim'
material or richer decorated output depending on the treatment of
tags. By default, tags are not active, hence the output is not
decorated with tag information. Once set_tags is set to true,
the pretty printer engine honours tags and decorates the output
accordingly.

When a tag has been opened (or closed), it is both and successively
'printed' and 'marked'. Printing a tag means calling a
formatter specific function with the name of the tag as argument:
that 'tag printing' function can then print any regular material
to the formatter (so that this material is enqueued as usual in the
formatter queue for further line-breaking computation). Marking a
tag means to output an arbitrary string (the 'tag marker'),
directly into the output device of the formatter. Hence, the
formatter specific 'tag marking' function must return the tag
marker string associated to its tag argument. Being flushed
directly into the output device of the formatter, tag marker
strings are not considered as part of the printing material that
drives line breaking (in other words, the length of the strings
corresponding to tag markers is considered as zero for line
breaking). In addition, advanced users may take advantage of
the specificity of tag markers to be precisely output when the
pretty printer has already decided where to break the lines, and
precisely when the queue is flushed into the output device.

In the spirit of HTML tags, the default tag marking functions
output tags enclosed in "<" and ">": hence, the opening marker of
tag t is "<t>" and the closing marker "</t>".

Default tag printing functions just do nothing.

Tag marking and tag printing functions are user definable and can
be set by calling set_formatter_tag_functions.

open_tag t opens the tag named t; the print_open_tag
function of the formatter is called with t as argument;
the tag marker mark_open_tag t will be flushed into the output
device of the formatter.

val close_tag : unit -> unit

close_tag () closes the most recently opened tag t.
In addition, the print_close_tag function of the formatter is called
with t as argument. The marker mark_close_tag t will be flushed
into the output device of the formatter.

val set_tags : bool -> unit

set_tags b turns on or off the treatment of tags (default is off).

val set_print_tags : bool -> unit

val set_mark_tags : bool -> unit

set_print_tags b turns on or off the printing of tags, while
set_mark_tags b turns on or off the output of tag markers.

Changing the meaning of standard formatter pretty printing

The Format module is versatile enough to let you completely redefine
the meaning of pretty printing: you may provide your own functions to define
how to handle indentation, line breaking, and even printing of all the
characters that have to be printed!

set_formatter_out_functions out_funs
Redirect the pretty-printer output to the functions out_funs.out_string
and out_funs.out_flush as described in
set_formatter_output_functions. In addition, the pretty-printer function
that outputs a newline is set to the function out_funs.out_newline and
the function that outputs indentation spaces is set to the function
out_funs.out_spaces.

This way, you can change the meaning of indentation (which can be
something else than just printing space characters) and the meaning of new
lines opening (which can be connected to any other action needed by the
application at hand). The two functions out_spaces and out_newline are
normally connected to out_string and out_flush: respective default
values for out_space and out_newline are
out_string (String.make n ' ') 0 n and out_string "\n" 0 1.

Changing the meaning of printing semantics tags

The tag handling functions specific to a formatter:
mark versions are the 'tag marking' functions that associate a string
marker to a tag in order for the pretty-printing engine to flush
those markers as 0 length tokens in the output device of the formatter.
print versions are the 'tag printing' functions that can perform
regular printing when a tag is closed or opened.

set_formatter_tag_functions tag_funs changes the meaning of
opening and closing tags to use the functions in tag_funs.

When opening a tag name t, the string t is passed to the
opening tag marking function (the mark_open_tag field of the
record tag_funs), that must return the opening tag marker for
that name. When the next call to close_tag () happens, the tag
name t is sent back to the closing tag marking function (the
mark_close_tag field of record tag_funs), that must return a
closing tag marker for that name.

The print_ field of the record contains the functions that are
called at tag opening and tag closing time, to output regular
material in the pretty-printer queue.

Multiple formatted output

typeformatter

Abstract data corresponding to a pretty-printer (also called a
formatter) and all its machinery.

Defining new pretty-printers permits unrelated output of material in
parallel on several output channels.
All the parameters of a pretty-printer are local to this pretty-printer:
margin, maximum indentation limit, maximum number of boxes
simultaneously opened, ellipsis, and so on, are specific to
each pretty-printer and may be fixed independently.
Given a Pervasives.out_channel output channel oc, a new formatter
writing to that channel is simply obtained by calling
formatter_of_out_channel oc.
Alternatively, the make_formatter function allocates a new
formatter with explicit output and flushing functions
(convenient to output material to strings for instance).

formatter_of_buffer b returns a new formatter writing to
buffer b. As usual, the formatter has to be flushed at
the end of pretty printing, using pp_print_flush or
pp_print_newline, to display all the pending material.

make_formatter out flush returns a new formatter that writes according
to the output function out, and the flushing function flush. For
instance, a formatter to the Pervasives.out_channeloc is returned by
make_formatter (Pervasives.output oc) (fun () ->Pervasives.flush oc).

These functions are the basic ones: usual functions
operating on the standard formatter are defined via partial
evaluation of these primitives. For instance,
print_string is equal to pp_print_string std_formatter.

printf like functions for pretty-printing.

fprintf ff fmt arg1 ... argN formats the arguments arg1 to argN
according to the format string fmt, and outputs the resulting string on
the formatter ff.

The format fmt is a character string which contains three types of
objects: plain characters and conversion specifications as specified in
the Printf module, and pretty-printing indications specific to the
Format module.

The pretty-printing indication characters are introduced by
a @ character, and their meanings are:

@[: open a pretty-printing box. The type and offset of the
box may be optionally specified with the following syntax:
the < character, followed by an optional box type indication,
then an optional integer offset, and the closing > character.
Box type is one of h, v, hv, b, or hov,
which stand respectively for an horizontal box, a vertical box,
an 'horizontal-vertical' box, or an 'horizontal or
vertical' box (b standing for an 'horizontal or
vertical' box demonstrating indentation and hov standing
for a regular'horizontal or vertical' box).
For instance, @[<hov 2> opens an 'horizontal or vertical'
box with indentation 2 as obtained with open_hovbox 2.
For more details about boxes, see the various box opening
functions open_*box.

@]: close the most recently opened pretty-printing box.

@,: output a good break hint, as with print_cut ().

@ : output a good break space, as with print_space ().

@;: output a fully specified good break as with print_break. The
nspaces and offset parameters of the break may be
optionally specified with the following syntax:
the < character, followed by an integer nspaces value,
then an integer offset, and a closing > character.
If no parameters are provided, the good break defaults to a
good break space.

@.: flush the pretty printer and output a new line, as with
print_newline ().

@<n>: print the following item as if it were of length n.
Hence, printf "@<0>%s" arg prints arg as a zero length string.
If @<n> is not followed by a conversion specification,
then the following character of the format is printed as if
it were of length n.

@{: open a tag. The name of the tag may be optionally
specified with the following syntax:
the < character, followed by an optional string
specification, and the closing > character. The string
specification is any character string that does not contain the
closing character '>'. If omitted, the tag name defaults to the
empty string.
For more details about tags, see the functions open_tag and
close_tag.

@}: close the most recently opened tag.

@?: flush the pretty printer as with print_flush ().
This is equivalent to the conversion %!.

Same as printf above, but instead of printing on a formatter,
returns a string containing the result of formatting the arguments.
Note that the pretty-printer queue is flushed at the end of each
call to sprintf.

In case of multiple and related calls to sprintf to output
material on a single string, you should consider using fprintf
with the predefined formatter str_formatter and call
flush_str_formatter () to get the final result.

Alternatively, you can use Format.fprintf with a formatter writing to a
buffer of your own: flushing the formatter and the buffer at the end of
pretty-printing returns the desired string.

Same as printf above, but instead of printing on a formatter,
returns a string containing the result of formatting the arguments.
The type of asprintf is general enough to interact nicely with %a
conversions.Since 4.01.0